© Smartboy10/DigitalVision Vectors/Getty Images CHAPTER 1 The Approach and Evolution of Epidemiology LEARNING OBJECTIVES By the end of this chapter the reader will be able to: ■ Define and discuss the goals of public health. ■ Distinguish between basic, clinical, and public health research. ■ Define epidemiology and explain its objectives. ■ Discuss the key components of epidemiology (population and frequency, distribution, determinants, and control of disease). ■ Discuss important figures in the history of epidemiology, including John Graunt, James Lind, William Farr, and John Snow. ■ Discuss important modern studies, including the Streptomycin Tuberculosis Trial, Doll and Hill’s studies on smoking and lung cancer, and the Framingham Study. ■ Discuss the current activities and challenges of modern epidemiologists. ▸ Introduction Most people do not know what epidemiology is or how it contributes to the health of our society. This fact is somewhat paradoxical given that epidemi- ology pervades our lives. Consider, for example, the following statements involving epidemiological research that have made headline news: ■ Ten years of hormone drugs benefits some women with breast cancer. ■ Cellular telephone users who talk or text on the phone while driving cause one in four car accidents. ■ Omega-3 pills, a popular alternative medicine, may not help with depression. ■ Fire retardants in consumer products may pose health risks. ■ Brazil reacts to an epidemic of Zika virus infections. 1 2 Chapter 1 The Approach and Evolution of Epidemiology The breadth and importance of these topics indicate that epidemiol- ogy directly affects the daily lives of most people. It affects the way that individuals make personal decisions about their lives and the way that the government, public health agencies, and medical organizations make policy decisions that affect how we live. For example, the results of epide- miological studies described by the headlines might prompt a person to use a traditional medication for her depression or to replace old furniture likely to contain harmful fire retardants. It might prompt an oncologist to determine which of his breast cancer patients would reap the benefits of hormone therapy, a manufacturer to adopt safer alternatives to fire retardants, public health agencies to monitor and prevent the spread of Zika virus infection, or a state legislature to ban cell phone use by drivers. This chapter helps the reader understand what epidemiology is and how it contributes to important issues affecting the public’s health. In particular, it describes the definition, approach, and goals of epidemi- ology as well as key aspects of its historical development, current state, and future challenges. ▸ Definition and Goals of Public Health Public health is a multidisciplinary field whose goal is to promote the health of the population through organized community efforts.1(pp3-14) In contrast to medicine, which focuses mainly on treating illness in sep- arate individuals, public health focuses on preventing illness in the com- munity. Key public health activities include assessing the health status of the population, diagnosing its problems, searching for the causes of those problems, and designing solutions for them. The solutions usually involve community-level interventions that control or prevent the cause of the problem. For example, public health interventions include establishing educational programs to discourage teenagers from smoking, implement- ing screening programs for the early detection of cancer, and passing laws that require automobile drivers and passengers to wear seat belts. Unfortunately, public health achievements are difficult to recognize because it is hard to identify people who have been spared illness.1(pp6-7) For this reason, the field of public health has received less attention and fewer resources than the field of medicine has received. Nevertheless, public health has had a greater effect on the health of populations than medicine has had. For example, since the turn of the 20th century, the average life expectancy of Americans has increased by about 30 years, from 47.3 to 78.8 years.2 Of this increase, 25 years can be attributed to improvements in public health, and only 5 years can be attributed to improvements in the medical care system.3 Public health achievements that account for improvements in health and life expectancy include the routine use of vaccinations for infectious diseases, improvements in motor vehicle and workplace safety, control of infectious diseases through improved sanitation and clean water, modification of risk factors Sources of Scientific Knowledge in Public Health 3 for coronary heart disease and stroke (such as smoking cessation and blood pressure control), safer foods from decreased microbial contam- ination, improved access to family planning and contraceptive services, and the acknowledgment of tobacco as a health hazard and the ensuing antismoking campaigns.4 The public health system’s activities in research, education, and pro- gram implementation have made these accomplishments possible. In the United States, this system includes federal agencies, such as the Centers for Disease Control and Prevention; state and local government agen- cies; nongovernmental organizations, such as Mothers Against Drunk Driving; and academic institutions, such as schools of public health. This complex array of institutions has achieved success through political action and gains in scientific knowledge.1(pp5-7) Politics enters the public health process when agencies advocate for resources, develop policies and plans to improve a community’s health, and work to ensure that services needed for the protection of public health are available to all. Political action is necessary because the government usually has the responsibility for developing the activities required to protect public health. ▸ Sources of Scientific Knowledge in Public Health The scientific basis of public health activities mainly comes from (1) the basic sciences, such as pathology and toxicology; (2) the clinical or medical sciences, such as internal medicine and pediatrics; and (3) the public health sciences, such as epidemiology, environmental health science, health education, and behavioral science. Research in these three areas provides complementary pieces of a puzzle that, when properly assembled, pro- vide the scientific foundation for public health action. Other fields such as engineering and economics also contribute to public health. The three main areas approach research questions from different yet complementary viewpoints, and each field has its own particular strengths and weaknesses. Basic scientists, such as toxicologists, study disease in a laboratory setting by conducting experiments on cells, tissues, and animals. The focus of this research is often on the disease mechanism or process. Because basic scientists conduct their studies in a controlled laboratory environment, they can regulate all important aspects of the experimental conditions. For example, a laboratory experiment testing the toxicity of a chemical is conducted on genetically similar animals that live in the same physical environment, eat the same diet, and follow the same daily schedule.5(pp157-237) Animals are assigned (usually by chance) to either the test group or the control group. Using identical routes of administration, researchers give the chemical under investigation to the test group and an inert chemical to the control group. Thus, the only difference between the two groups is the dissimilar chemical deliberately introduced by 4 Chapter 1 The Approach and Evolution of Epidemiology the investigator. This type of research provides valuable information on the disease process that cannot be obtained in any other way. However, the results are often difficult to extrapolate to real-life situations involving humans because of differences in susceptibility between species and dif- ferences in the exposure level between laboratory experiments and real- life settings. In general, humans are exposed to much lower doses than those used in laboratory experiments. Clinical scientists focus their research questions mainly on disease diagnosis, treatment, and prognosis in individual patients. For example, they try to determine whether a diagnostic method is accurate or a treat- ment is effective. Although clinicians are also involved in disease preven- tion, this activity has historically taken a backseat to disease diagnosis and treatment. As a consequence, clinical research studies are usually based on people who come to a medical care facility, such as a hospital or clinic. Unfortunately, these people are often unrepresentative of the full spectrum of disease in the population at large because many sick people never come to the attention of healthcare providers. Clinical scientists contribute to scientific knowledge in several important ways. First, they are usually the first to identify new diseases, the adverse effects of new exposures, and new links between an exposure and a disease. This information is typically published in case reports. For example, the epidemic of acquired immune deficiency syndrome (AIDS) (now called HIV for human immunodeficiency virus infection) officially began in the United States in 1981 when clinicians reported several cases of Pneumocystis carinii pneumonia and Kaposi’s sarcoma (a rare cancer of the blood vessels) among previously healthy, young gay men living in New York and California.6,7 These